Multiple Line Graphs — Prelims Strategy

Prelims Strategy

Read the legend and determine whether the vertical axis gives levels, percentages or indices. Write down the actual dates for the interval being compared. Calculate change per unit time when the question asks for a rate and intervals differ; do not rely on visual steepness alone.

For percentage growth, use the earlier observation as the denominator. For an indexed series, interpret a movement from 100 to 125 as a 25% increase relative to that series' base, without assuming equality of original quantities across series. If the question asks when two lines are equal, distinguish equality at an observed point from an estimated crossing between points.

Use interpolation only when the problem explicitly permits it. A straight segment drawn between two observations is not sufficient evidence that the underlying quantity changed uniformly. Check whether the requested answer is an exact value, an average rate or an estimate. Finally, avoid attributing one series' movement to another merely because they rise together; the graph provides a pattern, not a controlled causal comparison.